It is known that certain biologically active compounds are better absorbed through the oral mucosa than through other routes of administration, such as through the stomach or intestine. However, formulations suitable for such administration by these latter routes present their own problems. For example, the biologically active compound must be compatible with the other components of the composition such as propellants, solvents, etc. Many such formulations have been proposed. For example, U.S. Pat. No. 4,689,233, Dvorsky et al., describes a soft gelatin capsule for the administration of the anti-coronary drug nifedipine dissolved in a mixture of polyether alcohols. U.S. Pat. No. 4,755,389, Jones et al., describes a hard gelatin chewable capsule containing nifedipine. A chewable gelatin capsule containing a solution or dispersion of a drug is described in U.S. Pat. No. 4,935,243, Borkan et al. U.S. Pat. No. 4,919,919, Aouda et al, and U.S. Pat. No. 5,370,862, Klokkers-Bethke, describe a nitroglycerin spray for administration to the oral mucosa comprising nitroglycerin, ethanol, and other components. An orally administered pump spray is described by Cholcha in U.S. Pat. No. 5,186,925. Aerosol compositions containing a hydrocarbon propellant and a drug for administration to a mucosal surface are described in U.K. 2,082,457, Su, U.S. Pat. No. 3,155,574, Silson et al., U.S. Pat. No. 5,011,678, Wang et al., and by Parnell in U.S. Pat. No. 5,128,132. It should be noted that these references discuss bioavailability of solutions by inhalation rather than through the membranes to which they are administered.
Ondansetron is a 5-HT3 receptor antagonist. The structure of ondansetron is depicted below:

Ondansetron is an anti-emetic used to treat nausea and/or vomiting, especially chemotherapy and radiation induced nausea and/or vomiting (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 260). Ondansetron is also used as a pre-operative anti-emetic (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 304). Administration of ondansetron in combination with a corticosteroid, such as phenothiazine or butyrophenone, can increase efficacy as an anti-emetic (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 928). Ondansetron can also be used to treat anxiety (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 427).
Ondansetron can be administered orally, intravenously, or intramuscularly. Ondansetron, when administered as an anti-emetic for severe chemotherapy-induced emesis, is typically administered at a single daily dose of 32 mg by intravenous infusion over about 15 minutes about 30 minutes prior to chemotherapy or intravenously in 3 divided doses of 0.1 to 0.15 mg/kg with the first dose given about 30 minutes prior to chemotherapy and the following doses given 4 and 8 hours after the initial dose. To treat severe chemotherapy-induced emesis, ondansetron can be administered at a daily dose of 32 mg in combination with a daily dose of 20 mg dexamethasone, each administered by intravenous infusion. For moderate chemotherapy-induced emesis, ondansetron is typically administered orally (as a tablet or solution) at a dose of 8 mg (tablet) or 10 mg (solution) about 30 minutes prior to chemotherapy followed by a second dose 8 hours later. The dose can then be repeated twice per day for 1 to 2 days following chemotherapy (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 928-930).
The oral bioavailability of ondansetron is about 60 percent with effective blood levels appearing 30 to 60 minutes after administration. Ondansetron is extensively metabolized by the liver with a plasma half-life of about 3 to 4 hours. Adverse effects of ondansetron are mild and include headaches, constipation, and dizziness (Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed., pp. 928-930).